Power efficiency is an important issue in wireless communication networks, for user equipment as well as for base stations. Depending on type of traffic and system behavior there are time intervals when the user equipment would not need to monitor a downlink control signaling channel all the time. Power savings could thereby be obtained at least in the user equipment. In order to determine such time intervals, the traffic needs to be predictable. In case of traffic types such as voice over Internet Protocol (VoIP), which is a fairly predictable type of traffic, an Adaptive Multi-Rate (AMR) codec can determine these time intervals with high accuracy.
In order to utilize the energy-saving potential of predictable traffic, the concept of discontinuous reception (DRX) has been introduced in LTE (Long Term Evolution), which allows the user equipment to reduce its power consumption. The basic mechanism of DRX is the configurable DRX cycle of the user equipment, wherein the base station transmits configuration parameters instructing the user equipment when to enter DRX mode. With a specific DRX cycle configured the downlink control signaling is monitored only in one sub-frame per DRX cycle and the receiver circuit of the user equipment is switched off in the remaining sub-frames, whereby the desired power saving is achieved.
In LTE, the time scale of the DRX mechanism can be aligned to a certain delay tolerance of the type of traffic at hand. For example, a long DRX cycle can be used in intermissions of a file download. That is, DRX can be applied in idle periods of the traffic flow. A short DRX cycle can be used for delay sensitive traffic types.
In High Speed Downlink Packet Access (HSDPA), Continuous Packet Connectivity (CPC) is introduced, which is a mechanism similar to the LTE DRX and used for achieving power savings in the user equipment.
From the above it is clear that efforts have been made in developing power saving modes such as DRX for user equipment. Such power saving modes should be as long as possible and preferably for different types of traffic and there is room for improvement in this regards.